1. Field of the Invention
This invention is in the field of cleaning hot gases along with heat recovery and is particularly directed to the treatment of hot coal gas from a coal gasification process wherein the coal gas is cooled down to such a degree that a final cleaning of the gas can take place at low temperatures.
2. Description of the Prior Art
The gaseous product of a coal gasification process produced, for example, in an iron bath reactor in which carbonaceous materials are converted in the presence of oxygen to form a coal gas essentially consisting of CO and H.sub.2 generally has a temperature between 1300.degree. and 1700.degree. C. The coal gas contains solid, liquid and gaseous contaminants. Both the high temperature as well as the necessity of removing the contaminants present in the coal gas present substantial problems.
Due to physical limitations, the coal gas can only be cleaned effectively at temperatures below 550.degree. C. and preferably should be cooled down to below 100.degree. C. Consequently, the coal gas must first be cooled effectively and then cleaned, and the sensible heat should be capable of being recovered at the same time.
Filters are known in the prior art in which the filter medium consists of a layer of bulk material which is resistant to high temperatures. This type of hot gas filtration, however, makes it nearly impossible to eliminate substances that do not become solid or liquid until lower temperatures are achieved in the gas. Beyond this, it is fundamentally extremely difficult to separate solid and liquid contaminants at high temperatures, since the dusts being formed are usually sticky and caking. Attempts to condense, solidify or desublimate the contaminants or other injurious substances in the product gas can produce considerable disruptions or reductions in useful life in the succeeding process stages during the cooling. For example, exhaust gas conduits and boiler surfaces can become caked and thus become less effective.
A method for hot gas dust removal is known from German Patent No. 24 24 932 wherein the coal gases of an iron bath reactor are subjected to a coarse dedusting. The disadvantages in this method reside in that fine contaminants in the coal dust cannot be removed and this applies particularly to the fine dust as well as to other components that are liquid or gaseous at high temperatures and only become solid or liquid at very low temperatures.
It is known from DE-OS No. 30 24 977 to conduct the coal gas of a coal gasification process through a heat exchanger whereby the product gas transfers its heat to the carbon carrier. This reference, however, provides no particulars regarding a dedusting or cleaning of the gases.
EP-OS No. 0054099 discloses a method and an apparatus for cleaning hot gases, particularly for steel and iron bath reactors, wherein the hot gases are cooled down to such a degree that a final cleaning at low temperature can take place in an electrostatic filter. There is no disclosure in this reference, however, as to how the heat exchange should take place. It is also silent as to how the particularly critical temperature ranges involved in the cooling can be traversed.